As is well known, a stabilizer bar is mounted on a vehicle such as an automobile for the purpose of suppressing tilting of a vehicle body, which is occurred at a turn or the like of the vehicle. Generally, the stabilizer bar is mounted to the vehicle body by means of a stabilizer bushing (vibration damping bushing). The stabilizer bushing includes a bushing body that is made of a tubular elastic body having an inner bore into which a stabilizer bar is inserted and a rigid bracket that is assembled to an outer circumferential surface of the bushing body.
It is well known that the stabilizer bushing used to mount a stabilizer bar to a vehicle body has problems of reduced driving comfort of the vehicle as well as generation of noise when friction between an inner circumferential surface of the bushing body and an outer circumferential surface of the stabilizer bar is big at the time of rotation of the stabilizer bar in a torsional direction (turn around its axis) in a state where the stabilizer bar is inserted into the inner bore of the bushing body.
In view of the above, various structures of the stabilizer bushing for reducing torsional friction generated between the bushing body and the stabilizer bar have been conventionally proposed. For example, JP-U-61-134411 proposes a stabilizer bushing having a structure in which a sliding member is fixed to an inner circumferential surface of a bushing body made of a tubular elastic body. The sliding member is composed of a liner cloth that is made of a cloth member including fluororesin fiber as a main component, for example. The stabilizer bushing having such a structure can lower the friction coefficient of the inner circumferential surface of the bushing body because of the presence of the sliding member. As a result, the torsional friction between the inner circumferential surface of the bushing body and the outer circumferential surface of the stabilizer bar can effectively be reduced.
Further, in the conventional stabilizer bushing, two partition members each having a semi-tubular shape are embedded in a middle area in a radial direction of the bushing body so as to divide the bushing body into an inner rubber portion, which is positioned at an inner side, and an outer rubber portion, which is positioned at an outer side, of the radially middle area of the bushing body. These two partition members are disposed in such a way that they correspond to each other in a longitudinal direction of the vehicle in a state where the stabilizer bar is inserted into the bushing body. Accordingly, in the conventional stabilizer bushing, the load applied to the bushing body by the relative displacement of the stabilizer bar in the longitudinal direction of the vehicle is dispersed by each of the partition members. Thus, excessive deformation of a part of the bushing body and permanent set, for example, due to the stress concentration, can be prevented.
However, the following problems are inherent in the conventional stabilizer bushing having the above structure.
Generally, in the conventional stabilizer bushing, the inner rubber portion is made to have a thin thickness such that the outer rubber portion has a big volume to the maximum extent possible, so that the damping characteristics against the load applied from the outside can be exhibited mainly at the outer rubber portion of the bushing body. Therefore, when the bushing body of such a stabilizer bushing is formed by vulcanization, unvulcanized rubber flow to both edges in a circumferential direction and both edges in an axial direction of each of the partition members, from a cavity section for molding an outer rubber portion, to enter the inside of a cavity section for molding an inner rubber portion having a small width, and then, the unvulcanized rubber flow a relatively long distance under a big flow resistance in the cavity section having a small width. Thus, the unvulcanized rubber does not perfectly fill the cavity section for molding an inner rubber portion, so that the thickness of the inner rubber portion may be varied.
In such a stabilizer bushing, when the sliding member is composed of a liner cloth having a surface lubricity, the liner cloth is generally fixed to the inner rubber portion at the time of vulcanization molding of the bushing body. Therefore, in the vulcanization molding of the bushing body of the stabilizer bushing, the following deficiencies may be occurred due to the flow pressure of the unvulcanized rubber that flow in the cavity section for molding an inner rubber portion which has a small width, under big flow resistance. Specifically, the liner cloth may be fixed to the inner rubber portion in a state where the liner cloth is partially undulated or rumpled, or a part of the unvulcanized rubber may be oozed from the inner circumferential surface of the liner cloth to form a rubber film thereon. If the above deficiencies are occurred, the sliding properties against the stabilizer bar are varied in the circumferential direction of the liner cloth. As a result, smooth rotation of the stabilizer bar in the torsional direction may be inhibited.
Further, in the conventional stabilizer bushing, the two partition members are disposed at the radially middle area of the bushing body such that they correspond to each other in the longitudinal direction of the vehicle, but no partition members are provided such that they correspond to each other in the vertical direction of the bushing body. Thus, in the case where the sliding member of the stabilizer bushing is composed of the liner cloth, both of the outer rubber portion and the inner rubber portion of the bushing body are elastically-deformed when the load in the vertical direction is applied to the stabilizer bushing in a state where the stabilizer bushing is mounted on the vehicle, whereby the liner cloth fixed to the inner circumferential surface of the inner rubber portion may be deformed or rumpled. Therefore, in such a case, the sliding properties against the stabilizer bar are also varied in the circumferential direction of the liner cloth. As a result, smooth rotation of the stabilizer bar in the torsional direction may be inhibited.